This invention relates to a non-asbestos disc brake pad for automobiles (hereinafter referred to as "disc brake pad").
As a braking system for automobiles, there are used disc brakes, in which a disc brake pad is used as a braking part.
Some known disc brake pads use asbestos (e.g. JP-A 49-21544, Junkatsu vol. 19, no. 9, p. 625-631 (1974)). In contrast, JP-A 2-132175 discloses a non-asbestos friction material which is a mixture comprising a fibrous base material such as metal fibers, inorganic fibers and organic fibers; a binder including a thermosetting resin such as a phenol resin; and as a friction adjusting agent a lubricant such as graphite, antimony trisulfide, etc, a powder of metal such as iron, copper, brass, etc., a filler such as barium sulfate, calcium carbonate, etc. and/or an organic friction adjusting agent such as cashew dust, acrylonitrile-butadiene rubber (NBR), styrene-butadiene rubber (SBR), etc. Such a mixture is subjected to molding with heating under pressure to give a disc brake pad.
But automobiles using these prior art disc brake pads generate a noise which is so-called "creep groan". This noise seems to be derived from the generation of stick slip vibration when a creep torque of an automatic transmission is applied to a disc brake, said stick slip vibration being resonated to produce a noise. The frequency of this noise is usually about 200 to 300 Hz. When a car is driven again after parking the car for a long period of time, particularly after parking (allowing to stand) the car overnight with a large change in temperature and/or humidity, the phenomenon of the creep groan occurs abruptly with a large amount at an initial stage of driving, which makes a driver uneasy and unpleasant.